The objective of this investigation is the development and application of biophysical methods to separate and isolate homogeneous tumor cell population from solid tumors in order to characterize their response in situ to radiation and/or other deleterious agents. Emphasis will be directed to characterizing these individual responses in order to determine in what manner, if any, they may interact and thus determine the eventual fate of a solid tumor treated in toto. The tumor systems which will be studied include: a methylcholanthrene-induced fibrosarcoma (FSa) and its in vitro growing clone FSA 1233, an L-P59 sarcoma, and a spontaneously arisen mammary carcinoma. The cell separation methods used include the separations of cells on the basis of their buoyant density by means of centrifugation and linear density gradients of either Renografin or Percoll, and on the basis of their size by means of centrifugal elutriation. Cell clonogenicity will be assayed in vivo using a lung colony assay and in vitro using standard tissue culture methods. Each of the separated tumor populations will be characterized with respect to selected kinetic parameters using the methods of isotope labeling, flow microfluorometry, and premature chromosome condensation in order to better understand its previous environmental situation in the tumor. Individual separated cell populations will also be studied to determine; a) response to radiation sensitizing electron-affinic drugs; b) response to hyperthermia; c) ability to repair potentially lethal damage; and d) age response to radiation and other therapeutic agents.